Embodiments of the present invention relate to lithium batteries and their structure, packaging and fabrication methods.
Lithium batteries are used in applications that require a small battery with a high energy density such as, for example, portable electronics, medical devices and space systems. A typical lithium battery comprises a support to hold one or more battery cells, each cell having a set of battery component layers that include an electrolyte comprising a lithium-containing material sandwiched between electrode layers, such as an anode, cathode, and/or current collectors. The battery component layers cooperate to store electrical charge and generate a voltage. Lithium batteries include larger scale structures, used for computer and car batteries, and thin film batteries in which the battery component layers are thin films which have thicknesses of less than 100 microns. Lithium batteries can also either be used individually or multiple batteries can be stacked together to provide more power or more energy.
Lithium battery structures and layouts that increase the energy density and specific energy of the battery are continually being developed. The energy density is the fully charged output energy per unit volume while the specific energy is the fully charged output energy per unit weight of the battery. In one example, higher energy densities and specific energies were achieved from thicker cathode layers, for example, cathodes having thicknesses of 5 microns or higher, which were deposited in a multi-step deposition and annealing processes, as described in commonly assigned U.S. Pat. No. 7,862,927, filed on Mar. 2, 2007, entitled “THIN FILM BATTERY AND MANUFACTURING METHOD”, to Krasnov et al. which is incorporated by reference herein and in its entirety. The thicker cathode films provided greater charge retention and faster charging and discharging rates even when the thickness of the other battery component layers were held constant.
However, while thicker cathode layers increase the energy retention levels of a battery, the thicker cathodes can generate other structural problems. For example, a thicker cathode can delaminate more easily during charge and discharge cycles because of variations in stress levels across the flat dimension of the cathode that result from varying lithium ion concentrations. The thicker cathode can also create fabrication and layout problems for the other battery component layers.
For these and other reasons, further developments and improvements in lithium battery structures, packaging and fabrication methods, which can provide high energy density and specific energy levels are continuously being sought.